In this section, the structural setting of the three siting regions within the framework of the tectonic setting of Northern Switzerland is described. In the context of the siting process for a deep geological repository, knowledge of the occurrence and architecture of faults is relevant as such structures may affect the properties of the rock volume. The following sections are focused on the siting regions and the framework of consideration is enlarged only sporadically. The chapter starts with a terminology section (Section 4.3.2), as structural geology terms might have slightly different meanings within different scientific communities. Section 4.3.3 provides an overview over the regional tectonic setting, with the focus on the larger tectonic structures such as the Konstanz – Frick Trough. Section 4.3.4 provides a description of the structures encountered during the characterisation of the siting regions, taking into account the interpretation of the 3D seismic reflection data and the observations from the recently drilled deep boreholes (Tab. 2‑1). A focused description of deformation in the Opalinus Clay is given in Section 5.5.

The general geological evolution of Northern Switzerland has briefly been introduced in Chapter 3. Section 4.3.5 elaborates on the tectonic evolution since Early Jurassic times in more detail and adds insights gained from the structural investigations during SGT Stage 3 and from recent investigations of the burial and temperature history by analyses of veins from outcrops and drill cores. Section 4.3.6 characterises key factors that influenced the present-day structural inventory in the siting regions. The chapter concludes with Section 4.3.7. Neotectonic activity (i.e. indications for post-Pliocene tectonic deformation) are discussed in Section 6.2.